The long-term objective of our proposal is to improve the efficacy of photodynamic therapy (PDT) for the treatment of solid tumors. PDT continues to be useful for the clinical treatment of a variety of malignancies. However, the procedure has not been optimized and tumor recurrences can occur. The rationale for this application builds upon recent preliminary data suggesting that a combined modality approach using a cyclooxygenase-2 (COX-2) inhibitor may improve PDT effectiveness. COX-2 is a rate-limiting enzyme in the biosynthesis of prostanoids and it is expressed in many tumors. Studies indicate that COX-2 expression is correlated with tumor survival, proliferation, and/or angiogenesis. Positive COX-2 expression in tumors has also been associated with poor clinical prognosis. These observations have led scientists to evaluate the role that COX-2 specific inhibitors can play in the prevention and treatment of tumors. We initially examined gene expression profiles following PDT in murine tumor cells and observed a 25 fold increase in COX-2 mRNA. We subsequently observed that biologically active COX-2 protein was significantly elevated above basal levels in tumors treated with non-curative PDT doses. This suggests tumor cells that escape eradication following PDT treatment may exhibit a pro-survival phenotype associated with COX-2 overexpression. Our pilot study also shows that adjunctive administration of a COX-2 selective inhibitor improves PDT mediated tumor killing, which further suggests that COX-2 expression may be an important determinant in PDT efficacy. We hypothesize that PDT mediated expression of COX-2 decreases treatment efficacy and that combining PDT with a COX-2 selective inhibitor will improve the therapeutic responsiveness of PDT. In order to better understand and optimize this novel combined modality approach we propose three specific aims: (1) to determine molecular mechanisms regulating PDT mediated COX-2 expression, (2) to determine how COX-2 inhibition improves PDT tumor response, and (3) to optimize procedures for enhancing PDT efficacy using a COX-2 selective inhibitor. If our preliminary findings are confirmed by studies outlined in this proposal, adjunctive COX-2 inhibitor treatment could provide a safe and effective method for improving clinical PDT.